1. Technical Field
The present invention relates to an illumination apparatus which illuminates, for example, an image formation element, a projector which projects and displays an optical image formed in the image formation element on a screen by means of a projection lens, and an illumination method, and more particularly, to a configuration of an illumination apparatus including a plurality of light source sections.
2. Related Art
As one of apparatus capable of displaying a large screen video, a projector which illuminates a small image formation element, which forms an optical image in accordance with video information, with light from an illumination apparatus, and displays in a magnified scale the optical image on a screen or the like by means of a projection lens has been put to practical use. With this kind of projector, the magnification, and the increase in luminance, of a projection image, and a reduction in luminance and color variations having been strongly demanded, a high performance illumination apparatus for realizing them has been developed.
For example, with a projection type display apparatus (a projector) disclosed in JP-A-6-265887 (refer particularly to FIG. 1), an increase in intensity of a light illuminating a light valve (an image formation element) is achieved by using two light source sections, and also, a reduction in luminance and color variations of an illumination light is achieved by providing an integrator system corresponding to each light source section. As the optical properties of all optical elements, such as the image formation element typified by a liquid crystal light valve, a polarizing element, or the projection lens, have an angle dependence with respect to an incident light, in order to achieve an increase in quality of a display image, it is desirable to use a light source section which can emit an illumination light having a narrow dispersion in angular distribution.
However, according to the configuration of this projector, as the two light source sections are disposed in positions quite distant from the illumination optical axis, the angular distribution of the illumination lights is widely dispersed, and also, two groups of light source images formed on the pupil plane of the projection lens are formed in positions distant from a projection optical axis. As a result, an reduction in contrast of the display image occurring, it is not possible to increase the luminance of the display image as much as hoped for. Also, as the imaging performance of the projection lens, being high in the vicinity of the projection optical axis, decreases with distance from the projection optical axis, it is not possible to sufficiently achieve the imaging performance of the projection lens, causing a display image degradation. Furthermore, in the event that the two light source sections differ in light emitting property, luminance and color variations caused by a differing way of the projection light being shaded due to the vignetting of the projection lens occur in the display image.
A projection type display apparatus (a projector) with which it has been attempted to solve these problems is disclosed in JP-A-2000-3612 (refer particularly to FIG. 1). An illumination apparatus used herein, including two light source sections, each of which, having a first focal point in the vicinity of a light emitter, is formed of an ellipsoidal reflector, has a configuration wherein a reflecting prism (a reflecting surface) is disposed at a second focal point of each ellipsoidal reflector, and a luminous flux from each light source section is reflected toward an integrator side by the reflecting prism. By this means, the positions of secondary light source images of the light emitters formed on the reflecting surfaces of the reflecting prisms are brought closer to an illumination axis than the original positions of the light emitters. As it is possible to handle the positions of the secondary light source images by taking them to be light source positions, it being the case that the two light source sections are disposed quite near to the illumination optical axis, it is possible to remedy the heretofore described problems.
However, in the illumination apparatus described in JP-A-2000-3612 too, the light source images formed on the pupil plane of the projection lens are still formed in positions distant from the projection optical axis. This is because, although the formation of the secondary light source image from each light source section in a position as near to the illumination optical axis as possible is nothing but the formation of each secondary light source image in a position as near to a vertex of the reflecting prism as possible, as the secondary light source images have a certain finite size, an appropriate area being required for the reflecting surfaces, it is not possible to reflect a luminous flux in the nearest vicinity of the vertex of the reflecting prism. Consequently, as it happens that a greater portion of the light source images does not exist on the projection optical axis on which a highest imaging performance is achieved in the projection lens, a greater effectiveness of remedying the problems can be hoped for than in the case of the projector disclosed in JP-A-6-265887, but this is not necessarily sufficient.